Tipton Kyle A, Rather Philip N
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA.
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
J Bacteriol. 2017 Jan 12;199(3). doi: 10.1128/JB.00705-16. Print 2017 Feb 1.
Recently, a novel phase-variable colony opacity phenotype was discovered in strain AB5075, where colonies interconvert between opaque and translucent variants. Opaque colonies become mottled or sectored after 24 h of growth due to translucent variants arising within the colony. This easily distinguishable opaque-colony phenotype was used to screen for random transposon insertions that increased the frequency of sectoring at a time point when wild-type colonies were uniformly opaque. A colony was identified that contained multiple papillae of translucent variants, and the insertion in this mutant mapped to an ortholog of the two-component system response regulator Subsequent investigation of in-frame deletions of and the sensor kinase (located adjacent to ) showed that the switching frequency from opaque to translucent was increased 401- and 281-fold, respectively. The mutant also exhibited sensitivity to sodium chloride in growth medium, whereas the mutation did not elicit sensitivity to sodium chloride. Mutation of either gene reduced motility in strain AB5075, but a mutation in both and produced a more profound effect. The and genes were cotranscribed but were not subject to autoregulation by OmpR. Both and mutant opaque variants were attenuated in virulence in the infection model, whereas mutation of had no effect on the virulence of the translucent variant. is a well-known antibiotic-resistant pathogen; many clinical isolates can only be treated by a very small number of antibiotics (including colistin), while some exhibit panresistance. The current antimicrobial arsenal is nearing futility in the treatment of infections, and new avenues of treatment are profoundly needed. Since phase variation controls the transition between opaque (virulent) and translucent (avirulent) states in , this may represent an "Achilles' heel" that can be targeted via the development of small molecules that lock cells in the translucent state and allow the host immune system to clear the infection. A better understanding of how phase variation is regulated may allow for the development of methods to target this process. The two-component system ortholog negatively regulates phase variation in , and perturbation of this system leads to the attenuation of virulence in an invertebrate infection model.
最近，在菌株AB5075中发现了一种新的相变菌落不透明度表型，其中菌落可在不透明和半透明变体之间相互转换。由于菌落在生长24小时后出现半透明变体，不透明菌落会变得斑驳或出现扇形区域。这种易于区分的不透明菌落表型被用于筛选随机转座子插入，这些插入会在野生型菌落均匀不透明的时间点增加扇形区域出现的频率。鉴定出一个含有多个半透明变体乳头的菌落，该突变体中的插入位点映射到双组分系统应答调节因子的一个直系同源物。随后对和传感器激酶（位于附近）的框内缺失进行的研究表明，从不透明到半透明的转换频率分别增加了401倍和281倍。突变体在生长培养基中也表现出对氯化钠的敏感性，而突变则不会引发对氯化钠的敏感性。任一基因的突变都会降低菌株AB5075的运动性，但和两个基因都发生突变会产生更显著的影响。和基因是共转录的，但不受OmpR的自动调节。和突变体的不透明变体在感染模型中的毒力都有所减弱，而突变对半透明变体的毒力没有影响。是一种众所周知的耐抗生素病原体；许多临床分离株只能用极少数抗生素（包括粘菌素）治疗，而有些则表现出泛耐药性。目前的抗菌药物在治疗感染方面几乎无效，迫切需要新的治疗途径。由于相变控制着从不透明（有毒力）到半透明（无毒力）状态的转变，这可能代表一个“阿喀琉斯之踵”，可以通过开发将细胞锁定在半透明状态并让宿主免疫系统清除感染的小分子来靶向。更好地理解相变如何被调节可能有助于开发针对这一过程的方法。双组分系统直系同源物负向调节中的相变，该系统的扰动会导致无脊椎动物感染模型中毒力的减弱。
